It is well-known that inter-and intra-winding capacitances limit the effective operation of high frequency voltage transformers. A circuit arrangement which in effect shorts out inter-winding capacitances is disclosed in Farnsworth U.S. Pat. No. 3,562,263. This circuit, known as the "diode split" circuit, utilizes multiple high voltage windings connected in series through diodes. The circuit, however, does not reduce intra-winding capacitances and in high voltage-high frequency power transformers so constructed the intra-winding capacitances become the limiting capacitance factors.
There are two generally employed ways to wind multiple winding transformers. The bobbin may be divided into sections by spacers parallel to its end plates and each section so provided wound in layers, or each layer may extend across the full width of the bobbin and successive layers are wound one on top of each other. The first type of winding is illustrated in Miyoshi et al., U.S. Pat. No. 3,843,903, specifically FIG. 7, and the second in Schreiner U.S. Pat. No. 3,886,434, specifically FIGS. 5A and 5B. In sectionalized windings the coupling between windings is not as close as it is in layer windings and the copper packing factor is somewhat less than is obtained in layer winding.
It has generally been the practice in layer winding of transformer coils to cover each layer with a strip of insulating material so as to provide a smooth surface for the succeeding layer. This construction permits the winding to be brought out as a lead at each end of the bobbin. However, unless the insulating strip is of appreciable thickness the surface of each successive layer becomes more and more irregular, so that the sequence cannot be used in a product environment when a large number of layers is required. If the separating strips are made thick enough and stiff enough to provide smooth winding surfaces the packing factor and the coupling are appreciably diminished.
It is also well-known that the maximum coupling between windings of power transformers is desirable. As the diode split circuit neutralizes the inter-winding capacitances of multiple layer windings it simplifies the design of such transformers. One arrangement is disclosed in the Schreiner patent previously mentioned. A single layer winding has the lowest intra-winding capacitance and if several single layer windings are superimposed and connected in the diode split circuit, the overall stray winding capacitance should be merely the individual intra-winding capacitances in series. Prior to my invention to be described hereinafter, however, no such winding arrangement with which I am familiar has fully realized the expected improvement. Those skilled in the art know that the intra-winding capacitance of a winding cannot be measured directly but can be calculated from the resonant frequency of the coil-intra-winding capacitance combination and the low-frequency inductance of the coil. Multiple layer power transformers so far constructed all have considerably lower resonant frequencies than would be expected from the measured resonant frequencies of their individual layer windings.